It is generally known to form or provide a primary selvage or fabric list along the edge of a woven web, as well as a temporary catch selvage outwardly alongside the fabric list, for different purposes. The fabric list or primary selvage remains a part of the finished woven fabric, while the secondary or catch selvage is used only temporarily during the weaving process and is then cut away from the woven web.
More specifically, in order to produce a high quality fabric having a durable fabric edge that resists unravelling and the like, it is known to bind or tie in the free ends of the weft threads along the edges of the woven web using so-called leno threads to achieve a full leno binding for forming a fabric list. Specialized rotational leno selvage forming devices have been developed for carrying out such full leno binding. German Patent 4,405,776 and corresponding U.S. Pat. No. 5,518,039 (Haeussler et al.), as well as German patent 4,405,777 and corresponding U.S. Pat. No. 5,524,678 (Haeussler et al.) disclose two different leno selvage forming devices that are capable of producing fabric list edges of the required quality and that are especially suitable for use with high speed looms, i.e. looms that carry out a very high weft insertion rate. The entire disclosure of each of the U.S. Pat. Nos. 5,518,039 and 5,524,678 is incorporated herein by reference.
The fabric list or permanent primary selvage is produced using so-called leno threads that bind in the weft threads on both edges of the woven web using known leno selvage forming devices. In high speed looms, it is especially suitable to use so-called reversible rotating leno selvage devices, which have reversibly rotatable leno disks or rotors that guide and manipulate the leno threads, such as the rotating leno selvage devices described in U.S. Pat. Nos. 5,518,039 and 5,524,678.
On the other hand, it has also been known to provide a secondary selvage or catch selvage strip for the following reason. While weaving a web on a loom, it is necessary to prevent a so-called spring-back of the free ends of a weft thread in a direction opposite the weft insertion direction, after the thread has been inserted and beat-up. Such spring-back of the inserted weft thread tends to occur due to the inherent elasticity of each inserted weft thread in the thread lengthwise direction. To prevent such thread spring-back, a so-called catch selvage strip is produced during the weaving process, in addition to and adjacent the above discussed fabric list or primary selvage, on both the weft insertion side and the weft arrival side of the loom shed. The purpose of the catch selvage strip is to securely bind in the free ends of the inserted weft threads to prevent the above mentioned spring-back during the weaving operation. After serving this temporary purpose, the catch selvage strip may be cut away from the woven web to produce the finished fabric.
In both air jet looms and mechanical gripper looms, the temporary catch selvage strip is conventionally formed using at least eight and up to twenty catch selvage threads, for firmly and securely binding in the respective ends of the weft threads. These catch selvage threads are stored and supplied wound up on catch selvage spools or bobbins, which therefore must be adapted to store at least eight and up to twenty catch selvage threads. By using this number of catch selvage threads, a relatively wide and thus material intensive catch selvage strip is produced.
It is also known to form the required catch selvage strip using a conventional multi-thread cross leno device, such as a so-called called four thread cross leno device. In this context, it is a disadvantage that the leno threads must be made of a material that is suitable for or adapted to withstand the mechanical loads placed on the threads in the cross leno device, for example due to significant thread deflections and the like. Thus, such leno threads must be made of a substantially break resistant material, for example a synthetic thread material. As a resultant disadvantage, the waste material arising from the trimmed catch selvage will not be composed of a single pure type of material, but rather will be a mixture of different materials. For example, the weft threads in the catch selvage strip typically comprise a natural material such as cotton or wool or the like, while the leno binding threads in the catch selvage strip are made of a synthetic material. It thus becomes difficult or impossible to reprocess or recycle the waste materials.
It is a further disadvantage, that the conventional multi-thread leno devices cannot keep up with a high loom operating speed, especially the high operating speeds that can be achieved by air jet looms. The operating speed of the loom and thus the production capacity is limited by the operating speed of the multi-thread leno device. If the multi-thread leno device is forced to operate at the higher loom operating speed, this results in premature wear of the machine components and therewith increased costs for maintenance, replacement and assembly. Furthermore, weaving faults are more likely.
As another disadvantage, the use of multi-thread cross leno devices often prevents the operation of an automatic removal and correction of weft faults such as weft breaks. If an automatic weft break removal is to be carried out, this requires the previously closed loom shed to be reopened and the weaving cycle of the loom to be operated in reverse. However, in such an operation, the catch selvage shed that has bound in the faulty weft thread is not always completely reopened, so that the faulty weft thread is not completely released from the catch selvage. For this reason, the weft fault removal or correction cannot be carried out with the desired efficiency.
Moreover, it is disadvantageous in the known arrangement, that the conventional cross leno devices produce the catch selvage strip in advance of the beat-up and binding point of the main loom shed, i.e. the beat-up edge of the woven web, in the direction of the catch selvage thread spool. It can be said that the cross leno devices pre-weave or pre-work the catch selvage strip ahead of the weaving of the fabric web. This is especially true on the weft thread arrival side of the loom shed, where the weft thread is subjected to a lower tension than at the weft thread insertion side.
Various further problems arise by using the two different kinds of devices or mechanisms for forming the fabric list or primary selvage on the one hand and the catch selvage on the other hand. As described above, rotating leno selvage devices, either with or without a reversible rotation of the leno rotor, are preferably used for high speed looms for forming very high quality woven web edges. On the other hand, for cost reasons and the like, the temporary catch selvage strips are formed using conventional leno arrangements and particularly multi-thread cross-leno devices, which are not suitable for use at high operating speeds due to the mechanical limitations thereof. As a result, the use of rotational leno devices for forming the fabric list, in combination with conventional catch selvage leno devices for forming the catch selvage, prevents the advantages of the rotational leno device from being fully achieved. Namely, while the high quality web edge is realized, the operating speed and therewith the output capacity of the loom are limited by the maximum operating speed of the mechanically operating catch selvage leno devices.